New evidence has been put forward suggesting that the Estonia ferry, which sank six years ago, was damaged by an explosion.

More than 850 people died when the ferry went down in the Baltic Sea in September 1994.

A representative of survivors and victims' families, who are pressing for a criminal investigation into the sinking of the ferry, said three separate sets of tests had been carried out on metal fragments recovered from the wreck by divers.

To us, it's now clear without a doubt that this hole has been caused by a detonation. There is no other possibility

Victims' families' representative

He said that distortion in the metal showed there had been an explosion.

The campaigners are not saying the explosion caused the sinking, but have sent their evidence to police in Sweden.

An official report in 1997 made no mention of an explosion. It said the ship's bow door, which had been missing a bolt, had been torn off in heavy seas.

Conflicting evidence

Lennart Berglund, chairman of a victims' families' association, said that an explosion could have occurred before or after the sinking.

"To us, it's now clear without a doubt that this hole has been caused by a detonation. There is no other possibility," he said.

Only 94 bodies were recovered from the wreck

Seismological data from the University of Helsinki seemed to have ruled out the possibility that an explosion could have caused the accident.

Records kept by the station, which can detect blasts caused by as little as 800 grams (two pounds) of explosives, showed no evidence of an explosion in the Baltic Sea on the day of the accident.

The three laboratory reports which reportedly show evidence of an explosion have been submitted to the Swedish authorities.

Sweden has agreed under pressure from victims' families to examine any evidence which conflicts with the 1997 findings.

Estonia and Finland have both insisted that they do not want to see the case reopened.

The Estonia was sailing from Tallinn in Estonia to Stockholm in Sweden in September 1994 when waves ripped off its visor-style bow door and water poured into the vehicle deck.

The ship capsized and sank off the Finnish coast, trapping most passengers inside.

Only 137 people survived the disaster, while 94 who managed to leave the vessel died in freezing water.